Although fluid valve and choke stem packings and wellhead lockdown screw packings constructed of elastomeric materials are known to be satisfactory for a variety of conditions, such packings do not provide the desired sealing function when subjected to high pressure gas environments, their failure being due to the phenomenon known as "explosive decompression". Replacing elastomeric materials with non-elastomers eliminates the "explosive decompression" problem, but non-elastomers creep when subjected to pressure and then do not return to their original condition when the pressure is removed, i.e., they have no memory. Due to the creep problem and the difference in the coefficient of thermal expansion of non-elastomers and the metallic packing gland and stem of a valve, conventional non-elastomeric stem packings leak after subjection to a pressure and temperature cycle.
In attempts to overcome the foregoing problems non-elastomeric lip seals have been provided with spring energizers to bias the sealing lips against the opposing metallic surface. Such a design is effective where the metallic surface is very smooth, but if the sealing lip is scratched or otherwise slightly damaged it will leak. Spring energized seals cannot be stacked in series to increase reliability unless a cartridge or other carrier is provided to contain them, but the carrier constitutes an undesirable additional part that adds to the cost, creates another potential leak path in the system, and necessitates enlargement of the packing gland and packing chamber.